As a convention seat for a vehicle, one that is described in Patent Document 1 is known, for example. In this seat for a vehicle, the frame is framed with general steels with superior workability, weldability and marketability. Then, in its framed state, it is made to be able to obtain a strength equivalent to high tensile steels by applying a heat treatment such as a high frequency hardening, a liquid carburizing, and a gas carburizing, to portions that require the strength where the stress is concentrated, or to that frame as a whole.